A number of electromechanical printer systems are now in use in which high speed repetitive operation of a multiplicity of hammer elements is used to control impacting at precisely timed intervals relative to a recording member. In such systems, prevention of erroneous hammer actuation and control of hammer movement are of crucial importance to print quality. In using the energization of a coil to effect printing action, it becomes highly desirable to have a regulated voltage source for supplying the multiple hammer energizing circuits, but it is of course not desirable to utilize expensive or complex circuits. It is desirable to avoid substantial power dissipation, and to protect against the generation of radio frequency interference and other noise effects in regulating the voltage. Furthermore, noise effects and transients within a system may introduce perturbations which cause erroneous hammer firings under various conditions, particularly during startup, shutdown and other intervals. It also can occur that there are various times at which it is desired to prevent possible firing of the hammers, as during paper advance intervals.